This paper intended to verify sex differences on the g factor (general intelligence) and specific abilities from a sample of children from two Brazilian cities: Belo Horizonte (BH) and Porto Alegre (PA). The sample from BH (n=1.316) aged 5 to 11 years was examined with a battery of intelligence (CPM, Verbal Scale of WISC-III, R-2), psychomotor (Bender) and school achievement tests. The sample from PA (n=779) aged 5 to 11 years was examined with Matrices Progressives Raven. The analysis from these tests shows that the majority of sex differences on specific abilities are not statistically significant. The use of Method Correlated Vectors, which is a most sophisticated method of analyzing general intelligence (g factor), indicates that there are no sex differences. These results support the international records about non-existence of cognitive difference relate to sex in childhood and adolescence.